[NQP Bump] Brings 11 commits

NQP bump brought: Raku/nqp@2018.05-57-g5f8cf42...2018.05-68-ga49b385a9
a49b385a9 [MoarVM Bump] Brings 3 commits
f70f77765 Merge pull request #462 from perl6/NOT_ACCEPTS
1139f7d43 Use kebab-case
efb316e55 Make the NQP optimizer convert +@ to nqp::elems(@)
85832d7f7 Add test for !~~
3aa04e360 Revert "Use faster nqp::elems instead of + on QAST nodes"
ee56eb3f4 Merge pull request #455 from jstuder-gh/chain_rm_decont
cf3cfb9ee Correct plan number
c9f84d39f Add test to make sure `return -1` works
c351d4349 [Impl] !~~by adding NOT_ACCEPTS method
c9fa8215f Remove erroneous decont op in chain compilation

tools/build/NQP_REVISION

@@ -1 +1 @@
-2018.05-57-g5f8cf42
+2018.05-68-ga49b385a9